Wireless communication system is widely used in urban and rural areas so as to provide communication services such as voice, video, grouped data, message delivery, broadcast, and the like. Wireless communication system may include a plurality of cells. The term “cell” used herein is referred to as the smallest region covered by a communication node and/or the subsystem of the node which serves the coverage region. Upon being powered on, or after losing a signal which covers the cell, a mobile terminal performs a cell search process to obtain information on a cell in which the mobile terminal is currently located, and the cell is referred to as a serving cell.
When in operation, the mobile terminal regularly measures the carrier signal intensity of BCCH (Broadcast Common Control Channel) of the serving cell and neighboring cells, so as to switch to another cell in time in which the signal intensity is higher than that in the current cell. And a list is created by obtaining system information of the serving cell. This list is known as a BCCH Allocation list or a BA list, which is associated with the assignment of the BCCH frequencies of the neighboring cells. The BA list, adapted for reselecting cells, includes a plurality of frequencies which are assigned by the wireless network and act as alternative frequencies for the mobile terminal. A mobile station measures and synchronizes the frequencies periodically, and receives system messages from BCCH for reselecting cells. The number of the alternative frequencies of the BA list is configured depending on the conditions of networks, namely, some networks have more alternative frequencies, and some have less. The BA list is stored in a permanent register or a SIM card of the mobile terminal, so that the mobile terminal searches for the frequencies in the neighboring cells based on the BA list when the mobile terminal is powered on. The mobile terminal detects the frequencies with a different interval when in an idle mode or in an active mode. While conducting a voice communication, the mobile terminal frequently searches for the frequencies in the neighboring cells, in order to switch to the frequency having the highest signal intensity to ensure an excellent voice quality.
In a conventional art, when the mobile terminal is powered on or switched to a new cell, every SIM card selects six frequencies having the highest signal intensity of the neighboring cells by using a generic sort algorithm. After 5 seconds, the SIM card re-selects another six frequencies of the neighboring cells by using the same sort method. However, when the mobile terminal does not change its position, the six frequencies selected within the previous 5 seconds are generally identical to the six frequencies selected within the later 5 seconds, or only a few of the six frequencies vary. Therefore, there is no need to rank the six frequencies each time. And nowadays, mobile terminals are functioned with multiple SIM cards, and each SIM card requires to create a BA list and to search for a multi-group of alternative frequencies, which causes a dramatic increase of operating data in the mobile terminal. If the conventional method for ranking frequencies is used, the response time of the mobile terminal may be affected greatly, resulting in poor operating performance of the mobile terminal.
A normal experiment result shows that there is little difference between two adjacent ranking results in a practical network.
In static cases (when the mobile terminal does not move), there are about 90 percent of cases that no more than two frequencies vary in two adjacent ranking results.
In dynamic cases (when the mobile terminal has moved), there are about 80 percent of cases that no more than three frequencies vary in two adjacent ranking results.
In the practical network, when a mobile terminal searches for the neighboring cells, generally, 10 to 20 frequencies may be found, and in the case of a mobile terminal with three SIM cards, even up to 60 frequencies may be found.
As a result, the conventional ranking method for reselecting six frequencies having the highest signal intensity every 5 seconds results in a waste in operating resource of the mobile terminal.